The present invention relates generally to a transmission hologram fabrication process, and more particularly to a novel transmission hologram fabrication process for fabricating various transmission holograms having a simple structure, a wide visible range and a large area.
The present applicant has filed a patent application (JP-A 06-308332) to come up with a hologram color filter that is a sort of transmission hologram. This hologram color filter is made up of a certain array of collective optical elements for collecting obliquely incident parallel light beams in a front direction. According to one typical fabrication process, the hologram color filter is fabricated by entering converging light from a collective lens and obliquely incident reference light into the same side of a hologram photosensitive material wherein the converging light and reference light interfere. According to another fabrication process, a computer-generated hologram (CGH) is used as a master hologram for hologram replication.
For the replication of such a transmission type of collective elemental hologram array as mentioned above, the present applicant has filed a patent application (Japanese Patent Application No. 07-249115) to propose a replication process for obtaining a hologram having the same hologram properties as those of a master hologram, wherein the master hologram is spaced away from a hologram photosensitive material by a distance equal to substantially twice as long as the focal length of each elemental hologram.
A transmission hologram scatter plate such as a transmission hologram screen, and a transmission hologram of a subject used for graphic art or the like is recorded by irradiating the front or back side of a scatter plate or a three-dimensional object that is the subject with illumination light and entering scattered light coming therefrom and reference light into the same side of a hologram photosensitive material wherein the scattered light and reference light interfere.
For the direct recording of a transmission hologram, it is thus required to enter object light coming from a transparent object corresponding to a subject (e.g., a collective lens or scatter plate) or a three-dimensional object and reference light into the same side of a hologram photosensitive material; in other words, it is impossible to record the subject while it is proximate to the hologram photosensitive material. For this reason, the resulting transmission hologram such as a transmission hologram scatter plate or graphic art has a limited visible range and so the range of the hologram, which can be observed by an observer, becomes narrow.
On the other hand, a hologram color filter is very clumsy to fabricate, because minute elemental holograms must be recorded in an array pattern while a collective lens is moved in a step-and-repeat fashion. For this reason, the hologram color filter is practically fabricated by preparing a master CGH and then applying this master CGH to a hologram replication process. However, it is not easy to fabricate large hologram color filters due to much difficulty involved in fabricating large master CGHs.
In view of such problems associated with the prior art as mentioned above, an object of the present invention is to provide a process that makes it possible to fabricate various transmission holograms having a simple structure, a wide visible range and a large area.
According to the first aspect of the invention, this object is achieved by the provision of a process for fabricating a transmission hologram which, when reconstructing illumination light is entered therein, diffracts a reconstruction wavefront in a direction opposite to the direction of incidence thereof, comprising steps of:
entering an object wavefront from a subject and a first reference wavefront into mutually opposite sides of a first hologram photosensitive material so that the object wavefront and the first reference wavefront interfere to record a reflection type of first hologram therein,
disposing a second hologram photosensitive material on a side of the first hologram on which the first reference wavefront has been incident for recording the first hologram, wherein first reconstructing illumination light is entered into the first hologram through the second hologram photosensitive material to diffract a reconstruction wavefront and, at the same time, a second reference wavefront having the same wavelength is entered into a side of the first hologram that faces away from the side thereof on which the first reconstructing illumination light has been incident at an angle deviating from a Bragg diffraction condition for interference fringes recorded in the first hologram to record a second hologram therein by interference of, at least, said reconstruction wavefront and transmission light of the second reference wavefront which has transmitted through the first hologram, and
disposing a third hologram photosensitive material on a side of the second hologram on which the first reconstructing illumination light has been incident for recording of the second hologram, wherein second reconstructing illumination light corresponding to the transmission light of the second reference wavefront that has transmitted through the first hologram for recording of the second hologram is entered into a side of the second hologram facing away from the third hologram photosensitive material to diffract a reconstruction wavefront to record a third hologram in the third hologram photosensitive material by interference of the reconstruction wavefront and transmission light of the second reconstructing illumination light that has transmitted through the second hologram.
Preferably in this aspect of the invention, the second reference wavefront for recording of the second hologram is the first reconstructing illumination light that has transmitted through the second hologram photosensitive material and the first hologram, and comprises a reflection wavefront reflected at reflecting means disposed on a side of the first hologram that faces away from the second hologram photosensitive material.
Preferably, the subject comprises a lens array, and said object wavefront comprises a group of converging wavefronts converged by respective lenses in said lens array.
Preferably in this case, the transmission hologram recorded in the third hologram photosensitive material by entering the second reference wavefront for recording of the second hologram into the second hologram photosensitive material at a given oblique angle of incidence is a hologram color filter.
Preferably, the first hologram is recorded as a Denisyuk type of reflection hologram of a reflective scatter type subject.
Preferably, the first hologram has been recorded as a reflection hologram of a scatter plate.
Preferably, the first hologram has been recorded as a reflection hologram of a transmissive body obtained by putting a lens array and a Fresnel lens on upon another.
Preferably, the transmission hologram recorded in the third hologram photosensitive material is used as a master hologram for hologram replication.
Preferably, the second hologram is replicated as a master hologram for hologram replication in the third hologram photosensitive material.
According to the second aspect of the invention, there is provided a process for fabricating a transmission hologram which, when reconstructing illumination light is entered therein, diffracts a reconstruction wavefront in a direction opposite to the direction of incidence thereof, comprising steps of:
recording a reflection type of first hologram in a first hologram photosensitive material using as object light a group of wavefronts converged or diverged by respective lenses in a lens array,
disposing a second hologram photosensitive material on a side of the first hologram on which reconstructing illumination light is incident, wherein the second hologram photosensitive material is irradiated with the reconstructing illumination light and, at the same time, reference light coherent with respect to the reconstructing illumination light is entered into a side of the first hologram that faces away from a side thereof on which the reconstructing illumination light has been incident at an angle that deviates from a Bragg diffraction condition for interference fringes recorded in the first hologram to record a second hologram in the second hologram photosensitive material by interference of the reconstructing illumination light, reconstruction light from the first hologram and transmission light of said reference light that has transmitted through the first hologram, and
disposing a third hologram photosensitive material on a side of the second hologram on which the reconstructing illumination light has been incident for recording of the second hologram, wherein reconstructing illumination light corresponding to the reference light for recording of the second hologram is entered into a side of the second hologram that faces away from the third hologram photosensitive material, so that a transmission hologram for reconstructing a group of converging wavefronts is recorded in the third hologram photosensitive material by interference of reconstruction light from the second hologram and transmission light of the reconstructing illumination light that has transmitted through the second hologram, and wherein:
for recording of the first hologram, illumination light is entered into a curved lens surface side of said lens array to create a group of object light wavefronts from said lens array, and a space between said lens array and said first hologram photosensitive material is filled up with a medium having a refractive index substantially equal to those of said lens array and said first hologram photosensitive material.
Preferably, the first hologram has been recorded with the first hologram located at a position substantially twice as long as a focal length of each lens in said lens array.
Preferably for recording of the first hologram, a light absorbing layer is interposed between said lens array and the first hologram photosensitive material.
Preferably in this case, the light absorbing layer has a transmittance of 50% or less.
Preferably for recording of the first hologram, a light absorbing layer is located on a side of the first hologram photosensitive material that faces away from said lens array.
Preferably in this case, the light absorbing layer has a transmittance of 50% or less.
According to the third aspect of the invention, there is provided a process for fabricating a transmission hologram which, when reconstructing illumination light is entered therein, diffracts a reconstruction wavefront in a direction opposite to the direction of incidence thereof, comprising steps of:
disposing a first hologram photosensitive material in front of a curved mirror array, wherein illumination light is entered into the curved mirror array through the first hologram photosensitive material to record a reflection type of first hologram therein by interference of the illumination light and a group of converging or diverging wavefronts reflected at respective mirrors in said curved mirror array,
disposing a second hologram photosensitive material on a side of the first hologram on which reconstructing illumination light is incident, wherein the second hologram photosensitive material is irradiated with the reconstructing illumination light and, at the same time, reference light coherent with respect to the reconstructing illumination light is entered into a side of the first hologram that faces away from a side thereof on which the reconstructing illumination light has been incident at an angle that deviates from a Bragg diffraction condition for interference fringes recorded in the first hologram to record a second hologram in the second hologram photosensitive material by interference of the reconstructing illumination light, reconstruction light from the first hologram and transmission light of said reference light that has transmitted through the first hologram, and
disposing a third hologram photosensitive material on a side of the second hologram on which the reconstructing illumination light has been incident for recording of the second hologram, wherein reconstructing illumination light corresponding to the reference light for recording of the second hologram is entered into a side of the second hologram that faces away from the third hologram photosensitive material, so that a transmission hologram for reconstructing a group of converging wavefronts is recorded in the third hologram photosensitive material by interference of reconstruction light from the second hologram and transmission light of the reconstructing illumination light that has transmitted through the second hologram.
Preferably for recording of the first hologram, a space between said curved mirror array and said first hologram photosensitive material is filled up with a medium having a refractive index substantially equal to that of said first hologram photosensitive material.
Preferably for recording of the first hologram, a light absorbing layer is located on a side of the first hologram photosensitive material that faces away from said curved mirror array.
Preferably in this case, the light absorbing layer has a transmittance of 50% or less.
Instead of said curved mirror array, a reflection type diffraction grating or a reflection type scatter plate may be used.
Thus, the transmission hologram fabrication process of the present invention comprises the first stage of recording the wavefront to be finally reconstructed in the form of the first hologram that is a reflection hologram with a wide visible range, the second stage of using the first hologram to record the second hologram that is a combined reflection and transmission hologram, and the third stage of recording in the third hologram photosensitive material only a transmission hologram for reconstructing only the wavefront recorded in the second hologram and desired to be reconstructed, and so enables a transmission hologram having a wide visible range and a large area to be easily fabricated. For instance, the process of the present invention can be applied to the fabrication of a hologram color filter without recourse to any CGH.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.